The present invention relates generally to a wheel revolution detecting device comprising a sensor rotor and a pickup sensor and serving as a wheel speed sensor in an antiskid brake system (ABS), etc. and more particularly, to the pickup sensor.
A wheel speed sensor, which has been conventionally used in the ABS for a motor vehicle, etc., comprises a gear-shaped sensor rotor fixed to a wheel side member such as a hub and having circumferentially continuous irregularities on its peripheral surface, and a pickup sensor fixed to a vehicle body side member such as a knuckle of a knuckle spindle, etc. The pickup sensor is generally provided with a magnet, a coil, and a soft iron bar therein, the soft iron bar protruding outwardly to serve as a detecting part, which is disposed adjacent to the irregularities of the sensor rotor with a predetermined clearance. With such a wheel speed sensor, the pickup sensor produces magnetic flux toward the irregularities of the sensor rotor through the detecting part, and detects a variation in magnetic flux in accordance with a revolution of the wheel side member, obtaining a revolution count of a wheel.
Two mounting structures of the wheel speed sensor have been proposed in the past. One is a parallel type where the ring-shaped sensor rotor having the irregularities formed on its outer peripheral surface is fixed on an outer periphery of a knuckle side end of the hub, and the pickup sensor is fixed to the knuckle so that a longitudinal axis of the bar-shaped detecting part is parallel to a face of the sensor rotor, perpendicular to a rotation axis thereof. Another is a perpendicular type where the pickup sensor is fixed to the knuckle so that the longitudinal axis of the detecting part is perpendicular to the face of the sensor rotor.
However, with the known mounting structures of the wheel speed sensor, i.e., the parallel or perpendicular type where an angle formed by the face of the sensor rotor perpendicular to the rotation axis thereof and the longitudinal axis of the detecting part of the pickup sensor is 0.degree. or 90.degree., a mounting space of the pickup sensor cannot be ensured in accordance with a layout of the hub, knuckle, brake rotor, drive shaft, etc.
Referring to FIG. 2, when a clearance A is small between a knuckle 12 side face of the hub 4 and a knuckle 12 side face of the brake rotor 6, for example, the pickup sensor 8 cannot be disposed parallel to the sensor rotor 7 fixed to the outer periphery of the knuckle 12 side end of the hub 4 since the brake rotor 6 and a splash guard 9 form a hindrance. It is noted that a face perpendicular to a paper face of FIG. 2 including a reference line L or a line parallel thereto corresponds to a face perpendicular to the rotation axis of the sensor rotor 7, i.e., the drive shaft S.
Referring to FIG. 3, in view of such conditions, a perpendicular-type disposition of the pickup sensor 8 can be adopted. In that case, due to requirements of increasing to a certain extent a clearance B between a tapped hole 61a of a flange 61 of the brake rotor 6 or tapped hole with which a bolt B.sub.2 for connecting the hub 4 and the flange 61 is engaged and an internal surface of the flange 61, and easy mounting/detaching of the brake rotor 6 to/from the hub 4, the outer diameter of the hub 4 cannot be enlarged, so that a main body of the pickup sensor 8 is disposed in the knuckle 12. This forms a hindrance to a motion of a base S1 of the drive shaft S or a sealing member SB between the knuckle 12 and the drive shaft base S1, resulting in impossible perpendicular-type disposition of the pickup sensor 8 without modifying a structure of the knuckle 12 and the drive shaft base S1.
Referring to FIG. 4, with the perpendicular-type disposition, in order to dispose the pickup sensor 8 without forming a hindrance to the drive shaft base S1 and the sealing member SB, the sensor rotor 75 having the irregularities on its inner peripheral surface can be mounted to the flange 61 of the brake rotor 6. In that case, however, the detection performance of the pickup sensor 8 may be lowered due to heat of the brake rotor 6.
Referring to FIG. 5, in order to dispose the pickup sensor 7 without forming a hindrance to either of the brake rotor 6 and splash guard 9, and the drive shaft base Si and sealing member SB, applicants have consideded angling, an angle C formed by a radial side face of the hub 4 and the longitudinal axis of the detecting part 82, to approximately 45.degree.. In that case, for obtaining the parallel-type disposition of the pickup sensor 8, the irregularities 76a of the sensor rotor 76 should be formed so that an outer peripheral circle thereof vary continuously in the longitudinal direction of the hub 4. Thus, the maximum outer diameter of the sensor rotor 7 is larger than that of FIGS. 3 and 4 to keep a predetermined thickness in a portion where the outer peripheral circle of the irregularities 76a is minimum, which forms a hindrance, resulting in difficult mounting/detaching of the brake rotor 6. Moreover, if the sensor rotor 76 has such a shape, the hub 4 should be thick to ensure the strength for holding the sensor rotor 76, resulting in a change in the shape of the hub 4.
Furthermore, with the mounting structure as shown in FIG. 5, if the mounting position of the hub 4 is axially shifted, a clearance is varied between a pointed end of the detecting part 82 of the pickup sensor 8 and the irregularities 76a of the sensor rotor 76, requiring a fine adjustment of the clearance when mounting the hub 4 is detached again.
It is, therefore, an object of the present invention to provide a wheel revolution detecting device that ensures excellent detection performance with a simple and rational structure and without any clearance adjustment.